What happens when paresthesia is elicited during spinal anesthesia?

What Happens When Paresthesia is Elicited During Spinal Anesthesia

When a paresthesia occurs during spinal needle insertion, you should immediately stop advancing the needle and check for cerebrospinal fluid (CSF) flow from the hub, as the paresthesia most likely indicates the needle has entered the subarachnoid space and contacted a spinal nerve root. 1

Immediate Clinical Significance

The paresthesia indicates intrathecal needle placement in 87% of cases. When transient paresthesias occur during spinal needle insertion, CSF is observed in the needle hub 86.7% of the time, confirming that the needle has successfully entered the subarachnoid space and contacted a spinal nerve root within it 1. This contradicts older teaching that suggested withdrawing and redirecting the needle away from the side of the paresthesia.

Proper Response Algorithm

• Stop advancing the needle immediately when paresthesia is elicited 1
• Remove the stylet and observe for CSF flow from the needle hub 1
• If CSF is present, proceed with local anesthetic injection as the needle is correctly positioned intrathecally 1
• Do not routinely withdraw and redirect the needle away from the paresthesia, as this is unnecessary in most cases 1

Risk of Persistent Neurological Complications

Paresthesia during needle placement significantly increases the risk of persistent paresthesia (P < 0.001), though the absolute risk remains very low. 2

Incidence and Outcomes

• Paresthesia occurs during needle placement in 6.3% to 13.6% of spinal anesthetics 2, 1
• Persistent paresthesia develops in approximately 0.04% of all spinal anesthetics (6 out of 4,767 cases) 2
• Among patients who experience intraoperative paresthesia, the risk of persistent symptoms is significantly elevated compared to those without paresthesia 2
• Resolution timeline: Most persistent paresthesias (4 of 6 cases) resolve within 1 week; the remainder resolve within 18-24 months 2
• No permanent neurological deficits were reported in the large retrospective series 2

Higher Risk Populations

Patients with known lumbar spine pathology experience paresthesias at significantly higher rates:

• 20% experience paresthesia during dural puncture (vs. 9% in patients without spine pathology) 3
• 16% experience paresthesia during injection (vs. 6% in patients without spine pathology) 3
• Despite higher paresthesia rates, no neurologic sequelae occurred in these patients, though the sample size was insufficient to definitively exclude increased neurologic risk 3

Clinical Pitfalls and Caveats

Common Misconceptions

Do not assume the paresthesia indicates epidural needle placement. While paresthesias can theoretically result from needle-to-nerve contact with a spinal nerve in the epidural space or within the intervertebral foramen with far lateral placement, the data demonstrate that most paresthesias occur when the needle contacts nerve roots within the subarachnoid space itself 1.

Warning Signs Requiring Immediate Action

Severe burning pain, dysesthesia not following dermatome distribution, or bladder/bowel dysfunction suggest direct spinal cord trauma rather than simple nerve root contact 4. These patients require:

• Immediate neurological examination 4
• MRI of the affected area 4
• Consideration of IV corticosteroids and NSAIDs to prevent inflammatory progression to arachnoiditis 4
• Avoidance of further spinal procedures 4

Documentation Requirements

When paresthesia occurs, document:

• The specific location and character of the paresthesia 2
• Whether CSF was obtained 1
• Whether the paresthesia was transient (resolved immediately) or persistent 2
• Patient's neurological status before discharge and at follow-up 2

Long-term Safety Profile

The overall safety of spinal anesthesia remains excellent despite paresthesia occurrence. In a series of 4,767 consecutive spinal anesthetics with 298 intraoperative paresthesias, there were zero cases of permanent neurological injury, demonstrating that transient nerve root contact during needle placement does not translate to clinically significant long-term harm in the vast majority of cases 2.